IC 485:a new candidate disk-maser galaxy at ∼100 Mpc distance. Milliarcsecond resolution study of the galaxy nucleus and of the H_2O megamaser
arXiv (Cornell University)(2023)
摘要
Masers are a unique tool to investigate the emitting gas in the innermost
regions of AGNs and to map accretion disks and tori orbiting around
supermassive black holes. IC485, which is classified as a LINER or Seyfert
galaxy, hosts a bright water maser whose nature is still under debate. Indeed,
this might be either a nuclear disk maser, a jet/outflow maser, or even the
very first `inclined water maser disk'. We aim to investigate the nature of the
maser by determining the location and the distribution of the maser emission at
mas resolution and by associating it with the main nuclear components of IC485.
In a broader context, this work might also provide further information for
better understanding the physics and the disk/jet geometry in LINER or Seyfert
galaxies. We observed in 2018 the nuclear region of IC485 in continuum and
spectral-line mode with the VLBA and the EVN at L, C, and K bands (linear
scales from 3 to 0.2 pc). We detected 2 water maser components separated in
velocity by 472 km/s, with one centred at the systemic velocity of the nuclear
region and the other at a red-shifted velocity. We measured for the first time
the absolute positions of these components with an accuracy of 0.1 mas.
Assuming a maser associated with an edge-on disk in Keplerian rotation, the
estimated enclosed mass is M_BH = 1.2 x 10^7 M_sun, consistent with the
expected mass for a SMBH in a LINER or Seyfert galaxy. The linear distribution
of the maser components and a comparison with the high sensitivity GBT spectrum
strongly suggest that the bulk of the maser emission is associated with an
edge-on accretion disk. This makes IC485 a new candidate for a disk-maser
galaxy at the distance of 122 Mpc. In particular, thanks to the upcoming radio
facilities (e.g., the SKA and the ngVLA) IC485 will play an important role in
our understanding of AGNs in an unexplored volume of Universe.
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关键词
galaxy nucleus,milliarcsecond resolution study,megamaser,disk-maser
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